Comment by krastanov | Hacker News Reader

Comment by krastanov | Hacker News Reader

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I think you are conflating two similarly named topics, or at least missing the point of why one of them is useful. At the risk of saying stuff you already know (do check the last paragraph for something you might not):

Quantum key exchange (only one of the applications of "quantum internet") is completely orthogonal to post quantum encryption.

Quantum key exchange is a way to distribute keys, which will be used in some symmetric encryption scheme that runs on classical computers. That scheme has security that does not depend on any "difficulty" conjectures. It is "information theoretically perfect" modulo implementation bugs. (Assuming Schroedinger's equation is not wrong).

This does not require the creation of a quantum computer. Actually it is much easier and already done in labs.

Post quantum encryption is just the name for asymmetric encryption algorithms that run on classical computers and are difficult to break on both classical and quantum computers.

Even though quantum key exchange is an exciting application of "quantum internet", way more interesting would be its use for the establishment of globe spanning entangled states. This can be used for the creation of sensors that surpass the diffraction limit and other practical "science stuff".

No. I think that is the exact point he was making that quantum key distribution is orthogonal to post-quantum cryptography and that the consensus is that poat-quantum cryptography will actually be used while quantum key distribution is basically an academic exercise because it doesn't have practical utility for the problem it is attempting to solve.

I am confused. How is "security that does not depend on any 'difficulty' conjectures / information theoretically perfect" not of practical utility?

The so called quantum key-exchange requires a shared secret, so it is actually doing key-expansion. Besides that it has practical problems in side-channel protection and cannot achieve a high enough bandwidth to be of interest in most practical settings.

If you wanted to toss out public key cryptography as insecure, I guess you could use QKE to make symmetric key cryptography more practical. You would have a secure method of communicating your keys, and wouldn't have to worry that your new post-quantum public key cryptography was broken- since symmetric cryptography just isn't vulnerable in the same way.

Edit: Deleted an incorrect comment. This is a good description of what I am missing: https://crypto.stackexchange.com/questions/2719/is-quantum-k... (man in the middle attacks)

Well, let's go...

> Quantum key exchange is a way to distribute keys, which will be used in some symmetric encryption scheme

The largest use of an asymmetrical cryptographic algorithm is key distribution, for use with a symmetric algorithm.

> That scheme has security that does not depend on any "difficulty" conjectures. It is "information theoretically perfect" modulo implementation bugs.

Up to this point, I've never seen any design of quantum encryption that provides any actual security. It's an abstract property of them that there should be one way to get physical security, just like it's a property of computing that there should be some good NP-hard problem one can base a cryptographic algorithm on. AFAIK, both are open problems.

To be honest, the only application for quantum entanglement I'm excited about is quantum teleportation.

Quantum teleportation is only useful for moving entangled states around- it's not actually useful in and of itself unless you have some other application for entanglement in mind.

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